1. Field of the Invention
The present invention generally relates to an antenna apparatus, and especially relates to an antenna apparatus that has a ground plate that is shaped like a plate, and a feeding unit that extends from the ground plate in a direction generally perpendicular to the ground plate at a predetermined offset angle for a predetermined length.
2. Description of the Related Art
In recent years and continuing, radio communications technology using UWB (ultra-wide band) attracts attention since radar positioning and communications with a large transmission capacity are possible. As for UWB, the U.S. FCC (Federal Communications Commission) allowed use of a 3.1-10.6 GHz band in 2002.
Communications at UWB are performed by sending a pulse signal using a wide frequency band. Accordingly, an antenna apparatus used for UWB has to be capable of receiving a wide band signal.
For UWB communications, at least in the 3.1-10.6 GHz frequency band approved by the FCC, an antenna apparatus consisting of a ground plate and a feeding unit is proposed (Non-patent Reference 1).
FIG. 1A shows a structure of a conventional antenna apparatus 10.
The antenna apparatus 10 shown in FIG. 1A includes a feeding unit 12 installed on a ground plate 11, the feeding unit 12 being shaped like an inverted cone.
In addition, the inverted cone that constitutes the feeding unit 12 is set up so that its side may form an angle θ to an axis 13 that perpendicularly intersects the ground plate 11. A desired property is obtained by the angle θ.
An antenna apparatus 20 shown in FIG. 1B includes a feeding unit 22 in the shape of a teardrop that includes an inverted cone 22a, and a sphere 22b inscribed in the inverted cone 22a on the ground plate 11.
“An Omnidirectional and Low-VSWR Antenna for the FCC-Approved UWB Frequency Band”, Takuya Taniguchi and Takehiko Kobayashi (Tokyo Denki University) (Announced on Mar. 22, 2003 at classroom B201) The Electronic Information Communication Society 2003 B-1-133.
However, since the conventional wideband-antenna apparatus is structured by the feeding unit having one of the inverted cone shape and the teardrop shape on the ground plate, the dimensions tend to be great. Then, an antenna apparatus that is smaller and thinner is desired.